Are “Low Temperature Rise” transformers more efficient?
One common misconception is that low temperature rise units are more efficient.
While they usually have better efficiency at full load, it doesn’t guarantee that this will be the case at lower loads.
Efficiency regulations typically use an average load of 35% to 50% when specifying efficiency. A low temperature rise transformer with more mass and surface area, but running with a low load may be less efficient and produce more heat than a standard transformer, while still maintaining a low overall temperature rise.
Core loss for low temperature rise units are higher than a transformer with the same kVA rating, but a higher rise (present whenever unit is energized).
Transformer temperature rise and efficiency should be regarded as two separate issues. If a high efficiency unit is desired, the TP1 (DOE 10 CFR Part 431), C802.2 (Canada) or NEMA Premium® energy efficient specifications should be noted. These regulations are all compatible with low temperature rise transformers.